S-(−)-9-Fluoro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-2,3-dihydro-7H-pyrido[1,2,3-de] [1,4]benzoxazine-6-carboxylic acid (levofloxacin, LVFX; JP 62-252790 A) is known as an excellent synthetic antibacterial agent.
There has been a compound known to be useful as an intermediate for producing this synthetic antibacterial agent, which is represented by the following formula (V):
wherein X1 and X2 each independently represents a halogen atom (hereinafter referred to as “Compound (V)”; similar symbolic marks will be applied to other formulae). This compound is known to be producible through the following process (JP 1-250369 A and JP 2-723 A).

That is to say, compound (V) can be synthesized by reducing compound (A), prepared beforehand by protecting the hydroxyl group of a commercially available lactic acid ester with a tetrahydropyranyl group, with lithium aluminum hydride to obtain compound (B), treating compound (B) and compound (C) in the presence of sodium hydride to obtain compound (D), and then removing the tetrahydropyranyl group, followed by reducing the nitro group.
The lactic acid esters serving as a raw material of compound (A) are commercially available at low cost, but the optical purity of such esters is limited to 97% ee at most, so they are not adequate as a raw material of the levofloxacin compound required to satisfy a high purity of at least 99% ee.
For the production of the compound (B), another process has also been developed without using any lactic acid ester (JP 2-265701 A). On the other hand, a large amount of lithium aluminum hydride is too difficult to handle for reduction, because of its safety problem. The aforementioned production process also demands relatively many steps. Furthermore, it has been reported that unnecessary recemization could be caused by the removal of tetrahydropyranyl group from compound (D) (S. Chladek, Chem. Ind. (London), 1719 (1964)).
Owing to the forgoing problems, several researches have so far been carried out using a compound ((R)-2-benzyloxypropionic acid ester) whose structure is close to compound (A) except that the tetrahydropyranyl group is replaced with a benzyl group. However, it has been impossible to obtain any compound other than those having a poor optical purity limited to 97% ee at most. Levofloxacin as a drug is required to have much higher optical purity of at lease 99% ee, but it is extremely difficult to improve the optical purity in intermediate steps. (R)-2-Benzyloxypropionic acid esters of 97% ee or less are not usable as raw materials for levofloxacin.
Hence, there has been a long standing demand for the development of a process not affected by these problems.
An object of the present invention is to provide an economical and efficient process for the production of an optically active propoxyaniline derivative and levofloxacin useful as an antimicrobial agent and also to provide processes for the production of intermediates for the foregoing process.
Another object of the present invention is to provide an enzyme having asymmetric ester-hydrolyzing ability and obtained by disrupting cells of a microorganism, which has asymmetric ester-hydrolyzing ability, under high pressure and then purifying the thus-disrupted cells successively by strong anion chromatography, hydrophobic chromatography and strong anion chromatography.